Etching process



June l2, 1945'. s. wALDMAN Erm. 2,378,052

ETCHING PROCES;

Filed Jan. 24. 1,1942 2 Sheets-Sheet l d///////// ////////.7// n 2l la L CI' L I'J l1 f I'I Il'lw---U--Ul'J-I 1 'Z' l-u-n-l U 1 E1 lr 2l 14 I;

-J f3 f i C' U f8 f7 mq I Q2 June l2, 1945. s. wALDMAN ETAL ETCHING PROCESS Filed Jan. '24. 1942 2 Sheets-Sheet 2 aaai/maza mum` o asvmanaad %|3H INV Sande Geo el''ogglma' BY @www ATTORNEYS UNITED STATES PATENT oFl-lcE 2,378,052 ETOBING Process Samuel Waldman and George F. Cenina, New Bedford, mignon Aerovox Corporation, New Bedford, Mass.

Appllcation January 24, 1942, Serlal No. 428,018

Claims. (Cl. 41-42i used in the manufacture of electrolytic condens- While the invention is not limited in its apers The present inven on is more especially plication to the etching of any particular metal concerned with a process and equipment for auor the use of any particular reagent it is particthe etching liquor is consumed and its concen` degree of etch desired.

tration reduced and the product of reaction is In the accompanying drawings, in which is increased, so that the gain in capacitance per illustrated the application of the invention in its unit iarea of foil being treated in such deterioratpreferred Held of use ing etching liquor drops progressively and the Fig. 1 is a plan view of an installation in which economy effected in condenser manufacture is the process maybecarried out,

lost, since more foil and more materials generally Fig. 2 is a side elevation thereof,

are required, as the high capacity gain per unit 26 Fig. 3 is an end elevation thereof,

oi' foil area is not assured for all of the foil being Fig. 4 is a graph illustrating the relationship etched. of temperature to recovery of distillate from the Among the objects of the invention are to prostill for an illustrative sample oi' etching reagent.

Vide a process by which etching may not only be and performed uniformly and reliably throughout, 3" Fig. 5 is a graph illustrating the percentage of requires no elaborate apparatus or skilled superf wherein the etching process is carried on in a in the proportion of contaminating salt and prod- 40 T over a series of rollers Il to a second reel (not with at substantially the same rate as fresh salt Cooling water is passed over the condenser from 2li. it passes into the tank etching process. The tank T also has connected thereto a vessel 2| containing a Iresh supply oi reagent, and the outlet 22 of which is adjusted to feed such fresh reagent at compensating rate. that is at rate corresponding to that at which reagent is depleted in the entire process. Water is also added at a replenishlng rate through a spigot (not shown). The concentrated salt liquor forming as an end product in kettle D may be drawn oli through drain valve 23 in the bottom of said kettle.

Liquor from the etching tank T, illustratlvely comprising an aqueous solution or dispersion of hydrochloric acid and aluminum chloride, is passed into the kettle D which is kept illled to a predetermined level, oi' slphon 24. The composition of the residue in the kettle will, of course, depend upon the temperature at which said kettle is maintained. The relationship of still liquor and distillate compositions at various still temperatures is illustratively indicated in the graph of Fig. 4 when an etching solution of 84.4 grams per liter oi hydrochloric acid and 36.5 grams per liter of aluminum chloride is fed to the kettle. As shown in the graph, the higher the temperature maintained in the kettle, the less its percentage of hydrochloric acid and the greater its percentage of aluminum chloride. For instance, if the kettle be kept at degrees F., the concentra tion oi hydrochloric acid therein will be much less than in the etching tank, i. e. about 4 grams per liter, while the aluminum chloride will have risen to 390 grams per liter hydrochloric acid in the distillate will have a concentration of 93 grams per liter.

While the etching liquor with a relatively high concentration oi the end product oi' reaction, in this instance aluminum chloride, would have poor etching efficacy, a concentratian of aluminum chloride in the etching liquor of between 35 and 40 grams per liter is used because it is practical and does not involve the high operating cost oi' keeping the aluminum chloride at a much lower concentration.

From the graph o! Fig. 5 it appears that where the liquor in the kettle is kept at 240 degrees F. about 98 per cent total hydrochlori-c acid in the feed is recovered. At 242.5 degrees F. 99 per cent is recovered and at 250 degrees F. recovery thereof is substantially 100 per cent.

The graphs show the operation with substantially a nine per cent aqueous solution of hydrochloric acid (84.4 grams per liter) containing 36.5 grams per liter of aluminum chloride, which is practical for many purposes, but similar graphs may be prepared to serve i'or carrying on the process with any other concentration of acid and salt.

Thus, ducted at any composition o! liquor substantially T for re-use in the in practice, the etching may be consuitable temperature, and the in the etching tank is kept \The collected volume of economical operating temperature and the distillate therefrom is returned to tank. That distillate remains uniform in composition as does also the concentration of aluminum chloride in the kettle. the excess of which is drained ofi continuously, the level of liquor in the kettle being maintained constant.

It will thus the process can oi technical supervision. The

in actual operation, with a minimum foil being and the recovered Vof depletion in the :,svaose at uniform temperature conditions through the etching tank. the composition in the tank remains substantially constant, since the'overilow causes withdrawal of the aluminum chloride at substantially the same rate as it is formed in the continued etching operation. Water and hydrochloric acid are returned to the etching tank after the distillation and only sumcie'nt adjustment with fresh material is required to make up for consumption and losses in the entire process.

In the kettle D the fairly concentrated liquor with its high content o! aluminum chloride is not diluted by the addition thereto o! liquor from the etching tank because such liquor, except for the equilibrium residue of aluminum chloride. is vaporized almost instantly by its contact with the hot concentrated liquor.

Inasmuch as the distillation of etching liquid produces a distillate oi! exceptional purity, it is possible to operate the etching process with make-up acid that is relatively impure. Such make-up acid, even though containing considerable amounts o! deleterious impurity, will have its harmful eilects reduced by its mixture with the much larger quantity of high purity distillate. Should make-up acid be so impure as to seriously impair the elcacy of the etching bath, then it should be introduced into the process in the tank overiiow or directly into the still kettle.

As many changes could be made in the above process and installation, and many apparently widely different embodiments oi this invention could be made without departing from the scope it is intended that all matter contained in the above description or shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent of the United States is:

l. The etching process which comprises treating the substance to be etched with etching liquid that has in solution any given percentage of etching reagent and any given percentage of the reaction product of said reagent, and maintaining substantial constancy of composition of said etchin solution throughout the etching procedure by withdrawing contaminated etching liquid therefrom to remove products of reaction entrained therewith at substantially the rate at which the latter are formed in the etching process, adding such withdrawn reagent to a body of liquid consisting of an aqueous solution containing a lesser proportion of etching reagent and a greater proportion of products of reaction than the etching liquid, while maintaining said body of liquid at a substantially constant elevated temperature for practically instantaneous and continuous distillation oi the vaporizable cornponent ci said added contaminated etching liquid. while discharging by overiiow from said body the undistilled residue oi said liquid, thereby to maintain the volume of said body substantially constant, returning the resultant distillate for further etching use, while adjusting the etching bath with fresh material at rate corresponding to that entire process.

2. The process of recovering etching reagent from solution, which consists in continuously withdrawing spent liquor from the etching process, delivering the liquor into a volume of liquid that has an aqueous solution of substantially the ingredients of the etching liquor but a much lower etching reagent content and a much higher content of reaction product, maintaining said volume of liquid at a temperature suillciently high for substantially instant distillation therefrom of the vaporizing constituent of the spent liquor as it is supplied thereto, and maintaining said volume substantially constant by continuously drawing of! by overilow the residual liquid fraction of such spent liquor, and continuously returning the distillate for re-use in the etching reaction, while adjusting the etching bath with fresh material at rate corresponding to that of depletion in the entire process.

3. The process of continuously recovering hydrochloric acid in the etching of aluminum, which consists in drawing oil the contaminated etching liquor at a constant rate, delivering the same to a body of liquid that has substantially the ingredients of the etching liquor including an aqueous solution oi' hydrochloric acid and aluminum chloride, but a much lower proportion oi' the former and a much higher proportion of the latter, maintaining the volume of said body of liquid constant by withdrawal therefrom in two fractions, a vapor fraction and a liquid fraction, conJointly at substantially the same rate at which etching liquor is supplied thereto, said fractionation and withdrawal being accomplished by maintaining said volume of liquid at a temperature sumciently high for substantially instant distillation of the more vaporizable component of said liquor as it is supplied to the volume. and disc the same for re-use while zeplenishing the material equivalent to 4. The combination recited in claim 3 in which the aluminum chloride content in the etching tank is maintained in the range of to 40 grams per liter and in which the Volume of liquid to which spent etching liquor is delivered has an aluminum chloride content in the order of 400 grams per liter and the hydrochloric acid content is in the order of 4 grams per liter, and in which said volume is kept at a temperature in the order of 250 degrees F.

5. The process of treating etching liquor throughout etching operation in order to maintain uniformity of etching efficacy and to reclaim etching reagent therefrom. which consists in maintaining the etching reagent and the products of etching reaction, each of predetermined concentration within the etching liquor, by drawing olf etching liquor throughout the etching operition to remove reaction products at substantially the same rate at which they are formed, conveylng the withdrawn etching liquor to a body of liquid of substantially ixed volume that has an aqueous solution of substantially the ingredients of the etching liquor but a much lower etching reagent content and a much higher content oi' reaction product, maintaining said body at a temperature sufficiently high to effect distillation of the vaporlzing constituents of said withdrawn liquor at substantially the rate it is added to the collected volume, continuously removing the residual liquid fraction of the added liquor by overflow, condensing the distillate and returning the condensed distillate for re-use in the etching Dl'eSS.

SAMUEL WALDMAN. GEORGE F. COGGI'NS. 

